Electric signaling system



June 5, 1945. E. w. DURKIN' 2, 7,

ELECTRIC SIGNALING SYSTEM Filed Sept. 28, 11 142 a Sheets-Sheet 1 EmaWESTALL oumuu Z ATTORNEY June 5, 1945. E. w. DURKIN ELECTRIC SIGNALINGSYSTEM Filed Sept. 28, 1942 3 Sheets-Sheet 2 INVENTOR ERIC WESTALLDURKIN ATTORNEY June 5, 1945. E. W. DURKIN ELECTRIC SIGNALINQ SYSTEMFiled Sept. 28, 1942 3 Sheets-Sheet I Wot I INVENTOR ERIOWEISTALLDURKIN.

KI'TORNE Patented June 5, 1945 tnnnermo smm esesmn Y Ene'wesmu 'Dnrkin,Ohisle'hurst, Englan as;

'signor to "SiemensBrothe donfEnglaniaBritish company IApplicationiseptember 28, 194-2, Serial N o.-45,9 ;911

"InGreat Britain Octoberlll, 1941 i n reclaims. (C1. ace- 84) lhiainvention rel-ates to electric signaling :systems and j is morenarticularly -conoerned 'with direct our-rent systems in which a sourceof current by which signaling is effected is situated at one end of thesignaling circuit over which signa1svane :to pass. Y

The invention maybe used alone fiorjsignale ing from one end of asignaling circuit to the .otherlorfl-it magi-be used in addition toother and differentlsignals normally transmitted over the circuit", e.g. impulses, ,to bring about some distinctiire operation at the distantor receiving end of .a circuit without the use of a wire or pathadditional itothenormal signaling mire-tor wires.

ltvis especially applicable [to the vtransn'iiss'ion or .a signal .bymanual means in that the a signal "is independent of theduration of amanualoperation provided lit i continues for .a long enough timewtoper'mitresponse .to the signal at the .re-

"Inj't'he present invention a signal is transnmittednin response to anaction taken at a .transnii'ttin-g point which brings about .amodification incomin i3 rectifiertinlrthe acircuit at the transmittingend to block the :current .flow in ithe line. Theis-i-gnalreceiving-relay =will thusrelease on the consequent reversal of the lineconnections theesignalreceiving relay tests the line and if ,-acciricuiti for current .is .found}the signal is accepted but if no suchcircuit exists then the release is notdue to-a signal but :to some othercause, e. g. an impulse of longer iduration or a ilisconnectionandfurther circuit changes at i the receiving point may take -placeconsequent: on ihelongerrelease of-rthe signal receiving relay.-Ihereversal is mos-tconveniently accomplished by a reversing relaycontrolled. directly or indi rectly byjthe signal receiving relay. Forinstance in one arrangement accordingly 110 the invention,

thelbneration .o'f fa @key throws a rectifier into thejsignalingciizcuitso as .to release the signal of jthe signaling circuit whereby apparatusat the receiving point caused to change itscondition and thereby anniilthe le'ffectsof the saidzmodificatioh atjthe 'transmittingpoint.Inorderfto accomplish 'this'fihe said anparatus on itschangereceivingrlay wherebylthereversing relay operates and locksindependently of any further -actionjby the imssignn "receiving relay.This anrangementlmay'be used in an automatic .tele; phone system, suchas La PABX, .for permitting access to vbe, cflo'tained to lines notavailable by dialling, such .asjunctiQn lines, by certain n-n-orprivileged subscribers who are provided at their of condition may haveas .its consequence circuitj changes which restore "the conditions inthe signaling circuit similar to these existing before the said actionwas taken, and these said conditions 'may :continue independently of thecontinuance 'of the action. The signal-is nreierab'ly made dependent onthe direction of current flow lathe-signaling circuit. The action takenintransmitting a "signal-may be the insertion of 'a block "in "thesignaling circuit or the removal "oi a block thereby bringing about thechange of condition such as "release or *opezation of a signal receiving'rel'ay at the receiving point. The block is conven- *iently "in theform of ==a rectifier and the-change of condition =o'f the "signalreceiving relay may bring about a reversal of -polarity of "the iineconnections-so that the eiiecig of thejblook or removal :is rovercome.mhis differs from impulsingslbyzreason "of the riactfthat it is tthereceiving apoaratus itself that idetemiinesithe and -onlyiclosed when itis wanted-tor use-such as is common in telephone systemsxandiwithisuchinstruments with a rectifier normallyshor't Cir? cuiteiifibyakey, asignal receiving relay being.

operated when a subscriberloopslthe line and released when thesubscriber throws the keyto insert the rectifier into "the circuitwhereupon .the

reversing .relay-is operated and locked to disconnect thesignalreceiving relay and local exchange apparatus --and connect thesubscriber's line to a junction, the connections now set up being suchthat-the rectifier is conductive to the polarity of thebatteryficonnections now obtained so that the "subscribers .loop isextended to'ithe junction] Similarlyanother facility may begiven tooer-t in privileged subscribers whereby they may intrude into busy localconnections, this facility-being agarovided alone or in addition to theaforementioned facility. For example; the atorementione'dsignalqeceiving line relay, after afiocal iconne'eti on hasbeenset u pand {the wanted subscriber "found busy, may be released by the insertionor the 'rectifier'into "the line circuit, the line relay son releasebringing about the operation 'of a changeover relay whereby the lineconnections are reversed 80111311931 the rectinervis conductiverand-permits :the signal receivingrelay to \reeoperate, and also-to bringabout lonerati'onief theswi-tching melanin connection to connect theirivileged party into the local :oon-l arrangements the signal may betransmitted by nectlon.

In a further arrangement according to the invention in order todistinguish between a signal and an impulse in an impulsing system. thesignal may be received on a high-speed signal receiving relay connectedin series with an impulse receiving relay of the ordinary type. Therelease of the high-speed signal receiving relay in response to theinsertion of therectifier into the line circuit brings about the linereversal and the test forthe existence of a circuit. If

current can flow the signal receiving relay is beclosed. The reversingrelay or a relief relay thereto may control circuit operations formaking effective circuits which are to be dependent sequence of whichthe signal receiving relay reoperates.

The particular arrangements mentioned above are illustrated in detail inthe accompanying drawings and are given only as examples of methodswhereby the present invention may be carried into efiect. In thedrawings the arrangements of Figs. 1 and 2 show the invention as appliedto providing certain facilities to privileged subscribers in telephonesystems of the automatic type, whereas Fig. 3 illustrates an aronimpulse reception. This arrangement of the impulsing the said lockingcircuit is not closed,

but is closed in response to a signal whereby a marking circuit isconnected to certain outlets in a level of a searching switch which iscaused to search for a free one of the outlets.

4 In a further arrangement of the invention the transmitting end of theline may be connected over oppositely connected rectifiers, one or otherof the rectifiers being short-circuited by contacts which on operationremove the short circuit from the one rectifier and impose it on theother. The signal-receiving relay at the receiving end of the line onreleasing brings about the operation or release of a reversing relay toreverse the connections. of the signal receiving relay to the line sothat the said relay 'will reoperate and so prepare the circuit at thetransmitting end for the insertion of the rectifier, at presentshort-circuited, on the transmission of another signal being required.This arrangement of the invention may be employed inan interactingsystem, for example, for providing the interaction between synchronousstepping of stepping switches, one being situated at each end oftheline, by arranging for the automatic reversal of the rectifierconnections at the transmitting point consequent on a discontinuance orreconnection of current in the line.

In a modification of the invention the blocking devices may take theform of resistances included in the signaling circuit at both thetransmitting and receiving points, the resistance at the former beingnormally short-circuited whilst that at the receiving point is efiectiveandof such a value that the signal receiving relay at the receivingpoint will operate in the signaling circuit when closed. For thetransmission of a signal the short-circuit across the resistance at thetransmitting Point is removed so that the resistance becomes efiectiveand causes'the signal receiving relay to release. On release the signalreceiving relay is adapted to bring about the short-circuiting of theresistance in the signaling circuit at the receiving point in con-'rangement whereby two step-by-step switches may be stepped insynchronism, and a switch at a receiving point made to assume a positioncorresponding to the setting of a switch at a transmitting point.

The arrangement illustrated in Fig. 1 ofthe drawings shows anapplication of the invention to a private automatic exchange (PAX) or aprivate automatic branch exchange (PABX)-, whereby subscribers or' onlyprivileged subscribers can obtain access to a junction without theintervention of an operator and/or whereby such privileged subscribershave a right-of-way facility whereby they can intrude at will into abusy local connection.

The arrangements illustrated in Fig. l, apart from the modificationsrequired to fulfil the features of the present invention, are similar tothose described in Fig. 1 of British application No. 5,709/41 andtherefore, only those parts of the latter arrangements necessary toenable an shown.

In Fig. lat the extreme left of the upper part of the figure isrepresented a privileged subscribers instrument TX connected over a pairof line wires to the exchange. This subscriber is shown as beingprovided; with both of the facilities above mentioned, that is, thesubscriber can obtain direct access to a junction line to anotherexchange and can also intrude into a busy local connection. 1 In one ofthe line wires is connected a metal rectifier MR, which is so connectedthat it will 0 oppose the flow of current over the line with the normalbattery conditions obtaining, that is, with a positive batteryconnection to the positive line wire and a negative battery potential tothe negative line wire. However, this rectifier is adapted to beshort-circuited by akey MEK when the key is in its normal or unoperatedposition. At the exchange the line wires are connected to an auxiliaryequipment AE comprising a line relay SR, a diverting relay R, and achange-over relay CO individual to the line. At the extreme right of theupper part of the figure is shown the subscribers line circuit .LC andits connection on the right to the bank contacts of line finders andupwards to the bank contact of connectors of an automatic switchingtrain over which calls are set up automatically.

In'the lower part of the figure is represented common apparatus which inits entirety may be identical with that illustrated in theaforementioned application No. 5,709/41, and therefore only a part ofthe apparatus necessary for the understanding of the present inventionis shown. This common apparatus has associated with it a junction overleads ME to another exchange, such as a public exchange. The jack EJ isa line jack on an operators switchboard by which the operator can make adirect connection to the subscriber TX. Y

name

in will be seen that thesubscriberfs line such a that having theinstrument isconnected over auxiliary :equipment AE and :the=lin-e jackEU to the line =circuit'LCwhich comprises a line relay TL and a cut-:ofirelay K, in the =manner well known to those skilled in'the art. Thespeaking wires, designated wand '17, the "test wire 1:, and theadditional wire .d are connected to contactsin the'banks of line findersto'thewipers of which are connected the'wipers of connectors,

the'bank oontacts of the connectors being mull tipled t1 and connectedto the several extension lines, for exampla'to wires a, b-,- and c, of"the line immediately; @n therelease ofrelay SR a-circuit havinginstrument TX. It is "to be understood that "when *the subscriber withthe instrument :desimes":tolmake a local call he removes his receivertherebymausing a line-finder to be taken I into use and'zstarte'd insearch o'fthe calling line.

when thi-s line is found "the canon relayK is operated and the connectoriinked to the line tinder taken into use :is: prepared to receivedialledimpulses. wanted subscribers number thereby setting the connector wipersto bankcontacts connected to *the wanted line anclthe called extensionis rung, I

all in known manner. Although the arrange -mentsan'd operations so fardescribed have as-.

sumed a'single link conn ection of line finder and connector thishasonly beendonefor the sake of simplicity it being possible for anintermediate switching stage or stages 'tobe provided so that The callerdialls the digits of the the line finder is linkedto a selector which*re- *scripti'on'will assume the simple line finder-connector link. Whenthe "line finder has been set and relay K operated earth isconnected'inthe liri-kcircuit to wire-c tohold relayK and "mark the lineengaged in the test'bank'of the connector and the jack EJ The connectortests thewanted Fline in the usual manner by'applying earth over itstest relay to the test "wiper, the test relay if "the line is free,operating in "series with the it cutofi relay and connecting alow'resistance earth to the test wire to mark the line engaged. If theline is found busyiwhen :testedfwire will be at earth "potential and thetest relay will not be operated and a busy signal will be reverted tothe caller.

In thenrrangements shown, anysubscriber if ailowedjuhction calls mayjbycalling'the operator, have his call set up by .her, but only some of the'subscribers'may .be provided with the key Mm for setting up junctioncalls directly. In the latter case the key is operated after thereceiver:has'beenremoved.

"Considering the circuit arrangement or Fig; .1

"in detail, it will be seen that when the receiver is removed atinstrument TX a circuit is closed from earth over Icontacts loft in'linelcircuit LC "contacts co5, upper pair of contacts of exten}sion"'jack EJ, contacts-f2, instrument TTX, key MEK, which in its normalor unoperated positi'onshort-circuits"rejctifier contacts 1:3,L1owerpair of contacts of jack "EJ, contacts co'fi'; relay SR, "contacts "k2,line relayL'to 'b'attery.fRelays SR. and L operate in this circuit.Relay SR at contacts srl "closes a circuit for -slow release relaySE-over contactscol.

Relay L in the line circu'itoperates andbrings about the operation or-line finders tohn'd "the calling'line, and if thecall-lea local-1oneit' procoeds in hammer pre vionslyh-eferred toand in known manner. li

' ltd-t is jafi'yunction call that is required "the subscriberdoesnotdial-but after the removalof the receiver operates the keyiMEIBI toopen the short-circuit across rectifier MR. "I t will be see'n that therectifier is soconnected asato oppose I' the flow-of "current inthe=circ11it--above described with the hattery oonnection "now"prevailing with the result the current ceases and relay SR relases an dopens the=-circuit of relay SBbut the latter relay be ing slow toreleasedoes not release is 'c1osed from 'ear th over contacts sr l rw l, s'b'lrighthand'winding 6f -diverting relay *R. to battery an-d relayRoperates. Contacts r2 and r3 'disc'omiect athe subscriber's line wiresfrom the line circuit LC and connect them to contactsin the hanks 2 and3 or the {junction tinder switch 'JF, thewipers of wh ichflaremonnectableto a junction--- over leads wlEr V Contacts 1"5 apply earthto the c leading to *the connector to render the line busy toothercalling subscribers and alsofito "operate relay in the line circuitto remove the battery ccnnections from the dine wires at-the flnder' andfurther to apply anengaging'potentiaJ tdithebh'sh of theiack EJ; Aholding circuit ior relay R 'is' -closed from earth over contacts coZ,T3, the subscriber-sloop 111-.

eluding rectifier contacts-r1, col', middle coil of'relay R, com-menlead -to the: junction finder enema-"contacts bhl, relay S to battery.Relay S nner-ates in this circuit *and connects up'the" circuit Tor thedriving magnet of the and *when -the wiper of this bank meets thiscontact the 'markingpotential "is extended over both Winamgsor grelay "Tin-series to an earth potential and relay T operatesg. (luntacts tlchange o'ver 'andthereby open the driving circuit'for the switch UF'ardshort circuit the lefthand high resistance winding and relay COtherefore operates in series with the right-hand low resistance windingof relay T, the potential of the outlets: bank l of *switch JF beingsuch as to render this outlet busy to other searching junctionfinders.Relay ficui-t gfor relay R a over" its middle winding; but,

as just stated,rlayfilltremains "held over its lefthand winding.Contacts cd3 opens a point z-in 2a oiireuit'ov'erwhich busy toneisapplied to the 1 calling subscriber in -the event of a junction circuitnot beingavailaible. "Iheremainihg contactspf :relay CO performs "-n-o'iunctions in the 'operationsmow T being described. Bythis time relays]; it will have released;

h' 'junction l'ine relay fn-ot shown) in-the junctio'n" finder -circuitoperates in series with the calling subscriber shoop and the junctionline a and causes the circuit to beheld in the "condition justdescribed. Itthehjunction is one leading-to anautomatic-exchangethesubscriber'can now proceed todial the digits of the wanted subscriberreplaces his receiver at 'I'X where- 7 upon the said junction line relayreleases and brings about the releaseof relays T, R, and K and therestoration of the circuits to normal.

The operations involved in the exercise by the privileged subscriber ofhis right-of-way facility for intruding into a busy local connection areas follows. For providing this right-of-way facility the wire d at anintermediate distribution frame is connected to a wire running to a bankcontact corresponding to the line in the banks of the finder. Thiscircuit includes a contact R3 of the cut-off relay K. Relay RW isconnected towire d and overa locking contact to wire c. 1 a

The subscriber at TX sets up a local connection to the wanted subscriberin the manner previously referred to. On a line finder fiinding thecalling subscribers line, relay K operates and an earthis applied to'thewire to lock relay K. Relays SR and SB are operated as before described.The subscriber dials the wanted number, relay SR remaining operatedduring impulsing owing to the slow releasing characteristics imparted toit by the shunting resistance and capacity.

If the wanted subscriber isfree, the call proceeds in the, usual manner.If however, the wanted line is busy when the connector is set to thewanted line, a circuitis closed from earth over contacts rw3, left-handwinding of relay RW, wire :1, contacts 703 and thence over winding (II)of the test relay H of the conneector to battery. Relay RW operates inthis circuit, but relay H does not. Relay RW locks over its righthandwriting and contacts rw2 to the earth on the 0 wire. Contacts .rwlprepare an operating circuit for relay CO over its left-hand winding,and contacts rw3 disconnectthe original operating circuit of relay RWover its left-hand windmg.

The privileged subscriber will receive busy tone, and if he wishes toexercise his right-ofway facility he operates the keyMIEK to remove theshort circuit from rectifier MR. Relay SR releases owingto theintroduction of the rectifier MR into the loop whereupon a circuit isclosed from earth over contacts srl, rwl, lefthand writing of relay COto battery and relay CO operates. Relay CO locks over contacts 002 andrwl and its left-hand winding. At contacts 005 and 006 the lineconnections are reversed resulting in a reversal of the batteryconnections to the rectifier MR so that current again flows in the linecircuit and relay SR re-operates. On the re-operation of relay SR anearth is applied over contacts srl and 004 to the d wire and thence overwinding II of the switching relay H in the connection resulting in theoperation of this relay and the switching through of the privilegedsubscriber to the wanted busy line whereby he canspeak to the wantedsubscriber.

When the conversationis finished and the priviledged subscriber replaceshis receiver, relay SR releases together with the line relay in theconnector circuit, and the connector circuit restores to normal. On theremoval of earth from the c wirethe cut-off relay K and relay RWarereleased. At contacts rwl relay CO is released. Thus the circuits arerestored to normal.

.It will be appreciated"--from:the foregoing that for coupling the linecircuit to the common coni a privileged subscriber can be provided with.either or both of the abovefacilities.

f Thearrangements is illustrated in Fig. 2 of the drawings showfltheinvention as applied to i the'provision of the privilege .tocertain'subscribers whereby access to a special group of outlets such asa junction group, which are not available by dialling or t othersubscribers not so privileged. In this arrangement the subscribers notso privileged. In this arrangement the subscriber having instrument. TXis provided with a special access key MEK which when it is not operatedshort-circuits a rectifier MR; and at the exchange with a line circuitLC includinga line switch LShaving access to several groups of outlets,some groups being accessible to all subscribers by dialling and anotheror special group which cannotbe reached by dialling but, only availableto privileged sub-e scribers by means of a signal, other than dialling,originated by the operation of the key MEK to remove the short-circuitfrom rectifier MR.

Thus the circuit arrangements are required to discriminate betweenselection by impulsing. and a signal originated by a privilegedsubscriber for obtaining the special group of outlets. The line switchLS may comprise a step-bystep or a motor driven uniselector, therectangle LSDM therefore representing either a driving magnet of astep-by-step switch having interrupter contacts in series with it, orthe latch magnet of a motor driven uniselector. This are rangement willbe fully understood ,by those skilledin the art without further detailedillustration or description. Also in the line circuit is a couplingrelay K, and a switching relay H.

Several of such line circuits are controlled from a control circuit 00connected in common to them. This circuit'CCC includes an impulsingrelay A, a signal receiving relay AQ and relay BQ and an auxiliary relayRQ, the three latter relays being of thehigh speed type. Also thecircuit includes release and dialling, relays B and C respectively, testand auxiliary test relays T and TA, and a marking relay G. The circuitalso includes a digit switch DS having a driving mag.- net DSDM andinterrupter contacts dsdm. Two levels dsl and (182 of the switch areshown, the former being concerned with the marking of groups in thelevel GL of the line switch LS according to the received digit, whilstthelatter is a homing level.

The coupling relay K in the line circuit LC is trol circuit when thelatter is free and in order to arrange that only one of the linecircuits atv a time can be coupled to the control circuit, individualconnections exist from each of the former through a contact b2 of therelease relay, Or a relief relay thereof, in the control circuit, to theoperating winding I of the coupling relay so that when the controlcircuit is engaged by one of the line circuits and the release relay inthe control circuit is operated, the operating windings I of the Krelays in all of the other line circuitsare disconnected. I

In the detailed description of the arrangements illustrated theselection of a wanted group accessible to all subscribers by diallingwill first be considered. 1

When the subscriber having instrument TX removes his receiver, a circuitis closed from earth over the left-hand windings of relays A and A62,contacts rql, h4, key M EK, instrument TX, contacts-h3, and thence overtwo circuits in paraim, one including contacts 112; operatingwindiTI-EI'GF relay-Etc battery; and the other includlays AQ-and lr tebattery. Relays. A, AQ, and K operate. Relay K at. contacts k5 appliesearth potential tothe: left-hand end of private wire P- terenderbusyqthe outlet to the calling subscriber ati therfi nal selector;at: contacts k4 prepares a ciring contacts l q-T and right-hand windingsof. re.

cult for the locking winding 11 of relay K, at

winding II of relay C, and driving magnetDS-DM; Relay 0 operates in thiscircuit.

but magnet DSDM is not'sufiiciently energised to attract itszarmature. iI

Relay 3-. at contacts b tprepares an impulsing potential on thisrwire.

circuit for magnet DSDM anduat contacts. 12.31 a

closes alo'cking circuit for relay K over itswind-r ing,IItandcontactsJc'L. .At. contacts 112 and simi-l lar contacts of'relay Bor; arelief relay thereof.

includedri-n. the circuitsofwindings I of relaysaK in the other linecircuits, the. operatlngcircuitsy forrelaysK are cpened so that no.other relay K cameperate... A circuitis. closed over contactsbl and aqlifor fully charging. condenser QA, while contacts 115 close in thecircuit for the line switch magnet LSDMrbut at this time contacts 02open so thatthiscircuitis not yet closed;

Relay 0 atcontacts cl furtherprepares the impulsing, circuit for magnetDSDM.

Qrrtherelease'o-f relay A tothe break period of. the first. impulse, acircuit is closed from earth over contacts a], 124, ct, winding II ofrelay C and magnet. DSDM to battery, and themagnet energises fully toprepare-for stepping. the wipers otswitchDS w i i Relay AQ also releasesand at contacts aql con nects the condenser QA in series with relays. BQand HQ, and these relaysbeing high-speed relays operateinthisdischargecircuit of the condenser.

However, thedischargein the condenser dissir patescomparatively rapidlyin this circuit and}. as thecharg eincondenser QA will dissipate beforerelay- AQ is reoperated no lockingv circuit for the relays can. beclosed over contacts aq,2,

and the relays will releasebefore the termination. of. thebreakperiodand re operation of relay AQ. Under these circumstances the short periodfor whichrelay BQ is operated is insufficient to-bring about theoperation of relayC, which is slow to operate, at contacts 'bqL Thisoperation will. occur. at each break period, but without any re: suit.The change. over of contacts. rql. and 12 new in the line circuit willhave no. effectas the in I brokenatthe home contactcf 161 611 ds2; butdue: to being slow to release, remains'oper ated, by the energisation orthez' winding throughout. the impulse train in the usual manner; v Thesubsequent impulses are registered by the switch. DS a. similar manner.Ontheterminationor theimpulse train relay 6 will release whereupon acircuit is? closed from earth over contacts tlz, 02'; b5; kzand' magnetLSDM? to battery. Ehema'gnetLSDM energisesin this circuit and the wipersof. the line switch arestepped: a

It: will bewseen that the contacts in level dsl;

areconnectedi over marking connections to-sepa rater groups of contactsto. different groups.- of outlets thelevel. GL of the line switch,'anc1' a further marking. circuit is-connectible overs contactsglr foraspecial 'group of contacts: to another group of outlets; The test. relayT is connectibl'e' teeny: one: or: these; former marking connectionsover" the level. dsli,.. whereas' it is directly con-f nectibl'e to the.special marlring connection ove contacts gt. V

It will be appr iciated: that those outlets? from theline switch. thatare free willl'have a .batl tery' potential on thevoutgoingfprivate wireP, whilst those thatare busy will have an earth Thus when the wiper oflevel? reaches the required group it will search over thiszgroupauntila. free outletis found where-w upon the battery potential on the privatewireis x extended. over contactsilcl, wipenand contact" level GL,marking. connection, contact. and. wiper level d'sl right andleft-handrwindings. or": relay in seriesntoearth and relay 'Ifwilloperate. It'

ti shortecircuit the.left-.handwindihg of relay T;

whereby. the potential." on the private contact or the outletisrloweredi and the. outletYthereby' marked busyyandflalso. removetheshort-circuitfrom: relay TA so. that this relay is permitted to operatein seriesiwith the magnet: LSDM which; is not nowsuflicientlyenergisedto continue thesteppin operations. r i r At contacts tal andover contacts 703. a. circuit is closed for: the switching relay Hwhichoperates relay operates to bring about the backward coir-w nection of anearthpotential to the fpriratewire to hold relay and busy thesubscribersucircuit.

and at contacts hl and. hZiloisksitself to the earth on the privatewire. Contacts 713 and h'4= release,

relays 'AQ and and extend the" positive and negative wirestolthecircuitahead wherein a line I is opened and? when relay. B releasesrelay Kisreleased at contacts. b3; and at contacts M a homing circuit is closedforthe 'digitswitch' DS" over itshoming level dsZ and contacts atand b-M"Thus the controlcircuit isrestbred to normal for immediate use byother-calls. The line circuit remains in the conditioncw ith relay Hoperated until the connection is relinquished when the earthfiis removedfrom 'the' private wire resulting in the release (ofrela'y Hand:therestoration ofthe line circuit to normal.

If a privileged subscriber requires connection to thesp'ecial group ofoutlets? after removinghisx receiver instead cf diallirrgh'e operatesthe key MEK' an'd int'roduces therectifler MR intowthe" loop circuit.The rectifier MRii-s so connected that it will" not permit current to.flowyin the circuit with the battery connections now prevail ingwith'the result that relayAQ releases. 1

At the contacts dq'l thecondenser QA, prev'rously fully-i chargedove'rcontacts: b l and aqtis connected'l iniicircuit with: relays? HQ and?RQ:

which-being fast operating relays operate imme'-' diately in thedischarge circuit for the condenser. Contacts rql and rq2 reverse thebattery connections to the line through relays AQ and A, theseconnections now being such that the rectifier MB is conductiveandcurrent again flows to re.-operate relay AQ. It is to be noted thatthe cessation of current in the circuitis only for the period it takesfor relay RQ to operate and this period will be shorter than the releaselag of relay A so that relay- A will not release.- Contacts aqZ arearranged to close before or almost immediately after contacts aql breakso that relaysBQ and.

RQ are locked in a circuit including contacts bl, M2 and aql. It'will beappreciated that these operations are extremely rapid and the lockingcircuit is closed before the current in the discharge circuit ofcondenser QA has fallen below that at which relays IBQ and RQ willrelease, as happened in the previous operations when selec-' tion wasaccomplished by dialling.

On the operation of relay BQ relay G operates, after its slow to operateperiod, over contacts byl, and at contacts gl marks the special group ofcontacts in the level GL of the line switch. Contacts g2 close thecircuit for magnet LSDM and the line switch searches for an outlet in,the special group. This and the subsequent opera tions are as beforedescribed and therefore will be fully understood, r

The arrangements illustrated in Fig. 3 are diagrammatic in characterand'indicate one manner of bringing about the synchronised operation" oftwo' step-by-step uniselectors and ensuringthat such'switches alwaysassume a position in line with each other such as may be required when anumerical setting oran operation which may be indicated numerically isto be transmitted from one point to a point remote from it, for example,between a transmitting pointTP and a-receiving point RP. 1

In the arrangements illustrated there is pro- 'vided at the transmittingpoint TP a uniselector DML having two levels dml I and dm l2 andstepping magnet DMLDM, and at the receiving point RP a uniselector DMAhaving levels dmal and dmaZ and stepping magnet DMADM, the requirementsbeing that these uniselectors should always 'move synchronously and bein line with each other. Both uniselectors are shown as being of thedirect drive type, but it will be appreciated by those skilled in theart that they may 'take an other known form.

The uniselector DML at the transmitting point TP is required to be setin accordance with a marking potential which may be applied over any oneof ten marking connections M to individual contacts in level dml I, itbeing arranged that when the wiper of the level is standing on a contactmarked over a marking connection a test relay T is operated, the relaybeing released when the marking is removed from the contact. The relay Tin conjunction with level dml2 controls a switching relay'S which isadapted to connect one or other of the rectifiers MBA- or MRB in a twoconductor line circuit extending between the two points whilst it shortcircuits the other rectifier. The rectifiers are connected in oppositesenses to one another.

At the point RP is an'impulse relay A over which battery is fed to theline circuit, and a reversing relay R which isadapted tojeffectreversals of the battery connections to the line over relay A. Relay :Ris controlled over level dmal and is connected to all of the even[contacts in the level. The contacts in level dmcL-Z' are individuallyconnected to signaling devices, such as lamps LD, which correspond innumber and position to the marking connections at point TP. It will beseen that with the circuit in the condition shown, that is, with theswitches DML and DMA having their wipers standing on the first contactsin their levels, andassuming that a marking potential exists on thefirst of the marking connections M relay T will be operated at point TPfrom the marking potentialover level dml I, whilst at point RP the firstof these indicatingdevices LD will be energised.

In level (217212 the odd contacts are commoned together and connected tothe back contact of change-over contacts ii the front contact of whichis connected in common to the even contacts of the level. Thus as relayT is operated and the wiper of level dml2 standing on the first contactin the level, relay S will not be operated. In consequence contacts slconnect rectifier MRB in series with the line circuit and short-circuitrectifier MRA. A circuit therefore exists, from I earth over the upperwinding of relay A, contacts rl, the lower line wire, lower winding ofrelay L, rectifier MRB, contacts sl, upper winding of relay L, upperline wire, contacts r2, lower wind-.

ing of relay A, to battery and relays Aand L are operated in thiscircuit. I

Relay A at contacts al maintain open the circuit for the stepping magnetDMADM. and contacts ll maintain open the circuit for relay LB.

In the event of themarking potential being removed from the first of themarking conneotions and applied to a later connection, relay T will bereleased. At contacts tl a circuit is closed for relay S over the firstcontact in the level dmzz' and relay S operates. At contacts sl therectifier MBA is included in the line circuit in place of rectifier MRB.This rectifier MBA is so connected as to prevent current flow in theline with the battery connections now prevailing and therefore currentflow ceases and relays A and L re lease.

At contacts Z'I an obvious circuit is closed for slow to release relayLB, and relay LB operates preparing a circuit for magnet DMLDM at contacts Z bl. At contacts al an obvious circuit is closed for the magnetDMADM of the switch DMA and the magnet energises and steps the wipersonto the next contacts (contacts 2) in their levels. The succeedingindicating device LD is operated over level dmal,

dmal and relay R operates. At contacts TI and 12, the battery connectionover relay A to the line is reversed, the connection of the battery tothe line being such that the rectifier MRA permits current to flow witha consequence that relays A and L re-operate. On the re-operation ofrelay L the circuit of relay LB is opened and a circuitv tain this relayoperated, the relay S remaining operated during the change over ofcontacts tl.-

Thus the two switches are lined up with each other, the wipers of bothbeing positioned on the second contacts in their levels.

If a marking potential had not been found on;

. An obvious circuit is closed for relay R over the second contact inlevel thesecond; contact of leyekdmltrfielay wimud nothavere -operated,andhirrconsequence wiper drill: the circuit: for relay S: would havebeen.

openedandLrelay-S released. At contacts s11- rec tifier MRB wouldagaiube connectcdin thelineand currentlfiow thereiniwould cease andrelays- A and. L be released 'withla consequentialstepping oiytheswitches asmbefore described; Such; opera ations would: continueuntilthe marked contacts inleveldmtt is foundr andrelay 'E operated, thecircuit coming w restwith relay S either operated or released. T usinlefiect the twoswitches DML andzDMAl interactz with and control-thestepping of one another; l

A modification of". this .arrangementrcan bezmad'ee for working:ouer'asingle: line wire earth re:--

tum. For eaample, two rectifiers: maybe individually connectable inopposite senses: to: thelinewire over-agjteversing contact (such as acontact of: relay S) and." at the other end. of the linen-the"- linerelay (such as relay' A) has a single coil thereof connected. in serieswithth'e: line and isconnecta hl'eover reversing contacts (such ascontactseflrelayR) to one or other of'two oppositeliy connectedbatteries. The operation of such scribed before will' be fullyunderstood. 4 A further manner which the present in- Y asim'plearrangement with what has been devention maybe employedfor'discriminating between an impulse of a regular impulsetrain and 1 asignal is to provide thatthe signal consists of a break periodofthe-line circuit longer than the break period of an impulse; Forexample, the line relayconnectedto the line over reversing contacts ofreversing relay; may" operate the usual release relay-which remainsoperated during the break periods of the impulses of an impulse train"The circuit oi the reversing' relay will include break contacts of therelease relay; these contacts remaining open solongas the release relayis operated, and closi'ngto complete the circuit of the reversing relaywhen therel'ease relay releases, the reversing relay thereupon operatingand? locking. The reversal of the" line circuit by the reversing relaywill bring about the opera tion of-the line relay and of the releaserelay.

thereby tocause said first means to leave. said certain position, andother means controlled by said first meansupon leaving; said certainposition for altering the connections ofsaid signaling circuit at saidreceiving point thereby tocause said first means to be controlled oversaid circuit to resume said certain position despite thepresence of saiddevice in said circuit.

2. A signaling system as claimed in, claim. 1,, wherein said other meansis effective to alter the connections of said. signaling circuit, onlyif the position of said first means remains changed for apredeterminedinterval oftime. l

3; Ina signaling system; a transmitting point and a receiving pointinterconnected by a Signaling circuit, a unidirectional currentconducting device at said transmitting point, means for connecting saiddevice into said circuit, a relay at said receiving point occupying acertain position and controlled over ma circuit m: change: itspositionrcsponsivatulsardrdezvicabeingiconnected intasaid; circuit,means: operated by said relay uporr changing: its. position. foraltering the: ceirnectinns of; saidsignalingrcircuit at, said receii ingpoint; therehy' -toc cause said: relay tol be con.-' trolled oversaidcircuitetor resume: said certain position despitertha presencenlof saiddevice; in said circuit, and said; relay effective upon; resumi ingzrsaid certain positionrtoi causeisaidrlastsmeans to maintainconnectionsaltered so said: relaywiii: remain; CEEtHFiHL posiit a:signalling? system; i at transmitting: point I and a receivingpoimtzinterccnnectezt: by a sig naling circuit, amidircctioriat:conducting device at said transmitting point; meansiflfor causing direchcurrent ta: flow over said circuit; meansfor: including: said device in?said circuit thereby I tovblock thezflow'of said' 'directcurrentthereover;.

' saidldeviceathereimw 1 5.1 In: a. signallina system; a transmittingpoint and: a: receivingrpointrinterconnected by a. signaling circuit,arunidircctional: current conduct ing device" at said transmittingpoint; a charged; condenserat said receiving: poinirmeansfior causingdirectcurrent tolflovc over'said signaling circuiir means. for includingsaid device in said-* circuitt to bloclrithe fiowv: of current:thereover, means aifsaidi receiving pointoperated' responsive to thecessation: of: said current flow-over said; circuit to cause. said:condenser to (discharge; a l-relay operatedl by: thedischarge of?saidicondenser and effective thereupon t aItenthe-connections of saidsignaling. circuit: atisaid receiving point, whereby direct"v currentiacaused to resume flowing: over said circuit despite. th -presence ofsaid device therein, saidithi rd means operated responsive to saidresumption of" current flow and" thereupon effective to maintain." saidrel ay' operated" independently of the discharge of said condenser.

6:. a signaling systemgwalunidirectional current? conducting device; acharged con-denser, a

signalingrcircuit, a source of direct-current volt for at other timesincluding said device in said circuit to block the flow of said current,means operated responsiveto wcessation otjthe' current flow over saidcircuit to cause said condenser to discharge; a relay" operated by thedischarge of said condenserandeffective *upon operation to reverse theconnection of sai'di source to circuit whereupon currentwillresumeflowing over said circuit it said cescation;wascausedby saiddevice: being included therein, and a locking circuit for relaycompleted by said third means only l't-Isaid. current-flow is resumed;before the charge on said condenseris dlssipatedi p 7; In: a"signaifng'system; aunidirectionalourrent conducting device, a "signalingcircuit, a source of" direct current voltage connected tosaid circuitforcausing current to flow thereover,

means for'atti mes opening said circuit; to-'inter rupt the-flow of saidcurrent, meansfor at other times including said device in said circuitto block the flow of said current, means operated responslve to thecessation of said current flow toreverse the connection of said sourceto said circuit whereupon current will immediately resume flowing ifsaid cessation was caused by said device beingincluded in said circuit,said last means efiective only if said current flow is thus immediatelyresumed for maintaining the connecton of said source reversed for solong as the current current immediately to resume flowing over saidcircuit if said cessation was caused by the operation of a particularone of 1 said interrupting means, said device being ineffective to causethe current to resume flowing over said circuit if said cessation wascaused by the operation of the other one or said interrupting means. I

9. In a signaling system,'a transmitting point and a receiving pointinterconnected-by a signaling circuit, means for causing current to flowover said circuit, two separate means at said,

transmitting point for interrupting the flow of current over saidcircuit, a device at said receiving point operated responsive to acessation of said current flow and efiective upon operation to causecurrent immediately to resume flowing over said circuit if saidcessation was caused by the operation of a particular one of saidinterrupting means said device being ineffective to cause the current toresume fiowingover said circuit if said cessation was caused by theoperation of the other one of said interruptingmeans, and another'deviceat'said receiving point operated responsive to a cessation of thecurrent flow in said signaling circuit if said cessation is ofpredetermined duration, the immediate resumption of said current flowunder control of said first device being effective to prevent said lastdevice from operating if the cessation was caused by operation of saidparticular one of said interrupting means. r

10. In a signaling system, a signaling circuit, a device having twopositions, means controlled by said device when it occupies one of saidpositions to render saidcircuit transparent to currenttending to flowthereover in-one direction and opaque to current tending to flowthereover in the opposite direction, said means controlled by saiddevice when it occupies the other of said positions to render saidcircuit'opaque to current tending to flow thereover in said onedirection and transparent to current tending-to flow thereover in saidopposite direction, a source of direct current connected to saidcircuit, meansoperated responsive to a flow of current over saidline'from said source to reverse the position of said device thereby toterminate'the flow of said current, and other means operated responsiveto, a cessation of the flow of current over said oircuit from saidsource to reverse the connections of said source to said circuit therebyto cause current from said source to resume flowing over said circuit.

11. In a system as claimed in claim 10,'means effective at times toprevent said second means from reversing the position of said deviceresponsive to a flow of current over said circuit.

"12. In {signaling system, a transmitting point and a receiving pointinterconnected by a signaling circuit, a device at said transmittingpoint having two positionsni'aans controlled by said device when it'occupies one of said positions to render said circuit transparent tocurrent tending to flow thereover in one direction and opaque to currenttending to flow thereover in the op posite direction, saidmeanscontrolled by said device when it occupies the other of saidpositions to render said circuit opegiue to current tending to flowthereover in said one direction and transparent to current tending toflow thereover in said opposite direction, a source of direct currentconnected to said circuit, ,means at said transmitting point operatedresponsive to a flow of current over said line from said source toreverse the position of said device thereby to terminate the flow ofsaid current, means at said receiving point operated responsive toiacessation of the flow or current over said circuit from said source toreverse the connections of "said source to said circuit thereby to causecurrentiirom said source to resume flowing over said circuit, said lasttwo, means interacting to cause current-,to

flow over said circuit pulsatingly, a switch at said i rality ofsubscribers stations each connected to said exchange by a line,switching apparatus at said exchange accessible to all of said stations,animpulse sender at each station for controlling said apparatus toextend calls thereover, other switching apparatus at said exchangeinaccessible to certain of said stations, each of the remaining stationshaving a unidirectional current carrying device and means for includingsaid device in the line outgoing from that station to said exchange, andmeans responsive to the inclusion of any one of said devices in itsassociated line for seizing said other switchingapparatus.

15. In a telephone system wherein connections between calling lines andcalled lines are extended over automatic switching apparatus and whereinsaid apparatus includes means normally preventing the completion of aconnection to any called line which is already engaged in anotherconnection, a unidirectional current carrying device associated with acalling line, means for including said device in said calling line'ifthe completion of a connection fromthat calling line to a, called lineis prevented due to said called line already being engaged, and means insaid switching apparatus operated responsive to said device beingincluded in said calling line and effective upon operation to cause thecompletion of said connection from said calling line to said engagedcalled line.

ERIC WESTALL DURIQN.

